Many transition metal complexes have been heretofore used as catalysts for organic synthesis reaction. In particular, metal complexes made of ruthenium metal and optically active tertiary phosphine have been well known as asymmetric hydrogenation reaction catalysts. Examples of ruthenium-optically-active phosphine complexes containing as a ligand an optically active tertiary phosphine such as 2,2-bis(diphenylphosphino)-1,1-binaphthyl include the following compounds: EQU Ru.sub.x H.sub.y Cl.sub.z (tertiary phosphine).sub.2 (A).sub.p
wherein A represents a tertiary amine, with the proviso that if y is 0, x, z and p represent 2, 4 and 1, respectively, and if y is 1, x, z and p represent 1, 1 and 0, respectively (JP-A-61-63690 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-63-135397); EQU [RuH.sub.r (tertiary phosphine).sub.m ]T.sub.n
wherein T represents ClO.sub.4, BF.sub.4 or PF.sub.6, with the proviso that if r is 0, m and n represent 1 and 2, respectively, and if r is 1, m and n represent 2 and 1, respectively (JP-A-63-41487, JP-A-63-145492); EQU [RuX.sub.a (Q).sub.b (tertiary phosphine)]Y.sub.c
wherein X represents a halogen atom; Q represents benzene which may have a substituent or acetonitrile; and Y represents a halogen atom, ClO.sub.4, PF.sub.6, BPh.sub.4 (Ph hereinafter represents a phenyl group) or BF.sub.4, if Q is benzene which may have a substituent, a, b and c each represent 1, if Q is acetonitrile, when a is 0, b and c represent 4 and 2, respectively, or when a is 1, b and c represent 2 and 1, respectively, and if the benzene having a substituent represented by Q is p-cymene and X and Y each are iodine atom, a, b and c each are 1 or a, b and c are 1, 1 and 3, respectively (JP-A-2-191289, JP-A-5-111639); EQU (Tertiary phosphine).sub.w Ru(OCOR')(OCOR")
wherein R' and R" each represent a lower alkyl group, a halogenated lower alkyl group, a phenyl group which may have a lower alkyl substituent, an .alpha.-aminoalkyl group or an .alpha.-aminophenylalkyl group or R' and R" together form an alkylene group; and w represents 1 or 2 (JP-A-62-265293, JP-A-63-145291); EQU RuJ.sub.2 (tertiary phosphine)
wherein J represents a chlorine atom, a bromine atom or an iodine atom (R. Noyori et al., J. Am. Chem. Soc., Vol. 109, No. 19, pp. 5856-5859 (1987)); EQU RuG.sub.2 (tertiary phosphine)
wherein G represents an allyl group or a methallyl group (J. P. Genet et al., Tetrahedron: Asymmetry, Vol. 2, No. 7, pp. 555-567 (1991))
However, even the use of these ruthenium-optically active phosphine complexes has found difficulties in practical use on an industrial basis. For example, these ruthenium-optically active phosphine complexes exhibit an insufficient catalytic activity or asymmetric yield. On the other hand, 4-methyl-2-oxetanone (also referred to as ".beta.-butyrolactone" or ".beta.-methyl-.beta.-propiolactone") has heretofore been used as a raw material of polymers. In recent years, 4-methyl-2-oxetanone has been noted particularly because its optically active form is useful according to JP-A-6-256482, JP-A-6-329768, JP-A-7-53694, JP-A-8-53540 and JP-A-8-127645.
As processes for the preparation of optically active 4-methyl-2-oxetanone there have been reported the following processes:
(a) Process which comprises subjecting 3-bromobutyric acid obtained by adding hydrobromic acid to crotonic acid to optical resolution with an optically active naphthyl ethylamine, and then cyclizing the product (J. Reid Shelton et al., Polymer Letters, Vol. 9, pp. 173-178, 1971; T. Sato et al., Tetrahedron Lett., Vol. 21, pp. 3377-3380, 1980);
(b) Process which comprises reacting an optically active 3-hydroxybutyric acid with triethylorthoacetic acid to obtain an optically active 2-ethoxy-2,6-dimethyl-1,3-dioxane-4-one which is then thermally decomposed (A. Griesbeck et al., Helv. Chim. Acta, Vol. 70, pp. 1320-1325, 1987; R. Breitschuh et al., Chimia, Vol. 44, pp. 216-218, 1990); and
(c) Process which comprises reacting an optically active 3-hydroxybutyric acid ester with methanesulfonylchloride for mesylation of the hydroxy group, hydrolyzing the resulting ester, and then reacting with sodium carbonate for condensation cyclization (Y. Zhang et al., Macromolecules, Vol. 23, pp. 3206-3212, 1990).
As a process for the preparation of an optically active 4-methyl-2-oxetanone in the presence of the previously mentioned ruthenium-optically active phosphine complex there has been reported the following process:
(d) Process which comprises the asymmetric hydrogenation of 4-methylene-2-oxetanone (also referred to as "diketene") in an aprotic solvent such as methylene chloride and tetrahydrofuran in the presence of [RuCl[(S)- or (R)-BINAP (benzene)]Cl or Ru.sub.2 Cl.sub.4 [(S)- or (R)-BINAP].sub.2 (NEt.sub.3) [in which BINAP represents 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, and Et represents an ethyl group] as a catalyst (T. Ohta et al., J. Chem. Soc., Chem. Cmmun., 1725, 1992)
However, these processes have the following disadvantages. In other words, the process (a) requires the use of a special optically active amine as an optically resolving agent in an amount equimolecular with the starting compound. Further, the process (a) subsidiarily produces an undesirable enantiomer in an amount equimolecular with the desired product. Thus, the process (a) is wasteful and economically disadvantageous.
The processes (b) and (c) are disadvantageous in that the optically active 3-hydroxybutyric acid or ester thereof as starting compound can be hardly synthesized. In other words, it is necessary that an optically active poly-3-hydroxybutyric acid ester in which microorganisms propagate themselves be thermally decomposed or 4-methylene-2-oxetanone be converted to acetoacetic acid ester by alcoholysis reaction before asymmetric reduction. This requires many steps and thus complicates the operation.
The process (d) gives solutions to most of the foregoing problems of the processes (a) to (c) but still leave something to be desired. In other words, the process (d) is disadvantageous in that the catalyst used exhibits a low activity, prolonging the reaction time. Further, the resulting product has an optical purity as low as 70 to 92% e.e. As reported in JP-A-6-128245, JP-A-7-188201 and JP-A-7-206885, this process has been improved. However, because of its low catalytic activity, this process leaves something to be desired on an industrial basis.